The invention relates to a method for the incorporation of an impurity in a solid state basic material, more particularly for doping and alloying semiconductor basic material, and an apparatus for carrying out this method.
The doping of semiconductor basic material for the production of semiconductor components such as diodes, transistors and thyristors, is carried out at the present time substantially in accordance with two known methods, that is to say diffusion technology and the so-called ion implantation method. The doping of n- and p-conducting semiconductor basic material respectively with trivalent and pentavalent impurity atoms for the production of a pn-junction using diffusion technology is described in detail for instance in publications of W. R. Runyan with the title "Silicon Semiconductor Data", A. Moeschwitzer with the title "Halbleiterelektronik" and H. F. Wolf with the title "Silicon Conductor Data". The doping brought about by so-called ion implantation is described for example in the article by E. F. Krimmel in "Internationale Elektronische Rundschau" 3/73 with the title "Mikroelektronik stoeszt in neue Dimensionen vor" and in a publication of L. Ruge and J. Frank with the title "II. International Conference on Ion Implantation in Semi-conductors".
Neither of the two prior art methods of doping is completely satisfactory since they have a series of disadvantages and are subject to specific limitations.
With the prior art diffusion technology, it is in principle only possible to diffuse into the semiconductor basic material only impurity atoms which are soluble in such basic material. Furthermore, in the case of the diffusion process there is a concentration profile of doping towards the interior of the semiconductor so that the depth of the diffusion layer is disadvantageously influenced. Further disadvantages of this known diffusion method lie in that owing to the breadth of the diffusion layer at the pn-junction parasitic capacitances appear and as a result the utility of the pn-junction is limited especially in the high frequency range. A further disadvantage is that the diffusion also progresses in the surface of the semiconductor material and that in the case of double diffusion the diffusion processes are not independent from each other and this is connected with the disadvantageous effect of the "emitter push". These disadvantages apply basically also for the further development of diffusion technology known as "field-aided diffusion", in the case of which the diffusion of the doping ions into the basic material is encouraged by an applied electric field. This development involved substantially a doubling of the diffusion coefficient without, however, the above-observed basic disadvantages of diffusion technology being dealt with.
The disadvantages of the prior art ion implantation method reside in that it requires a large expenditure as regards apparatus and more particularly that on bombardment with the high energy ions crystal lattice faults are produced which must be removed later on by heat treatment, and that there is a particularly strong dependence of the depth of penetration of the ions on the orientation of the crystal.
These defects in the case of the prior art doping methods have led to a substantial requirement for doping techniques based on another principle. The aim of the invention is the creation of a method for doping or alloying semiconductor basic material, and generally for the incorporation of any impurity in a solid state basic material, which while keeping to a realistic expenditure as regards apparatus makes possible a selective doping, which can be exactly monitored or controlled as regards the extent in area and depth of penetration, of impurity substances into the basic material while obtaining the sharpest possible doping profile and can be modified in a very simple manner to suit the many different conditions and circumstances in accordance with the various doping substances and basic materials.